1. Field
This invention relates generally to the storage, transportation and disposal of highly radioactive components, and, more particularly to apparatus for vertically segmenting a boiling water reactor control rod blade to facilitate storage and/or transportation.
2. Description of Related Art
One type of commonly used boiling water nuclear reactor employs a nuclear fuel assembly comprised of fuel rods surrounded by a fuel channel. Each fuel channel of a boiling water reactor typically consists of a hollow, linear, elongated, four-sided channel of integral construction, which except for its rounded corner edges, has a substantially square cross section. Commonly, each channel is roughly 14 feet (4.27 meters) long by five inches (12.7 cms.) square and laterally encloses a plurality of elongated fuel elements. The fuel elements are arranged to allow for the insertion of a cruciform shaped control rod, which, during reactor operation, is movable vertically to control the nuclear reaction. As is generally known, the control rods come in a number of similar shapes, e.g., an American version, a Nordic version and a German version, and generally include an upper portion having a handle and four upper ball rollers for guiding the upper portion of the control rod as it moves vertically and a lower portion comprising a lower casting that in at least one of the versions functions as a velocity limiter and lower ball rollers that serve as a lower guide for the vertical movement. The main body structure, between the upper and lower portions, includes four blades or panels which extend radially from a central spline. Preferably, the blades extend longitudinally to at least a height that substantially equals the height of the fuel elements, which is approximately 12 feet (3.66 meters). The width of the control rods at the blade section is approximately twice the width of the panels, which is in the order of 10 inches (25.4 cms.) and the blades are approximately 2.8 inches (7 mils.) thick.
Following functional service, boiling water reactor control rod blades are difficult to store and dispose of because of their size, configuration, embrittled condition, and radiological activity. Heretofore within the United States, in-pool storage of control rod blades has been extremely space inefficient and dry cask storage is not readily available. The control rod design may vary with the manufacturer, but the four-panel design with the panels radially extending from a central spline at 90° intervals around the circumference of the control rod is common to all of the boiling water reactor designs, and thus, a common storage problem.
Control rod blades and other irradiated hardware are typically Class C low level radioactive waste as defined and determined pursuant to 10 CFR §61 and related regulatory guidance e.g., NRC's Branch Technical Position on Concentration Averaging and Encapsulation. Since Jul. 1, 2008, low level radioactive waste generators within the United States that are located outside of the Atlantic Compact (Connecticut, New Jersey and South Carolina) have not had access to Class B or Class C, low level radioactive waste disposal capacity. Lack of disposal capacity has caused boiling water reactor operators considerable spent fuel pool overcrowding. Though currently very uncertain and subject to numerous regulatory and commercial challenges Class B and Class C, low level radioactive waste disposal capacity for the remainder of the United States low level radioactive waste generators is anticipated in the relatively near future.
One technique for reducing the volume of boiling water reactor control rods for spent fuel pool storage has been to sever the upper and lower portions of the control rods from the control rods' blades. In the remaining main blade structure, the individual blade sections have been removed from the central spline by longitudinal cuts and the severed parts are then stacked for storage or burial as described in U.S. Pat. No. 4,507,840. This type of process requires three approximately 4 meter long cuts with handling time in between that makes this an arduous process. The packing of the segmented blades is also inefficient leading to high customer costs. An alternate approach has been taken in U.S. Pat. No. 5,055,236, which suggests that a vertical cut be made along the center line of the spline to divide the control rod blades into two chevrons. The chevrons can then be closely stacked for storage. Each of the approaches yields 12-foot (3.6 meters) or longer segments that are costly to shield and transport. U.S. Pat. No. 4,507,840 recognizes that since the blades enclose neutron absorber rods, which contain radioactive gas, the vertical cuts must be made quite near the central spline to avoid releasing the radioactive gases. Thus, horizontal segmentation of the blades, which would cut across the sealed rods that contain the neutron absorber material and the radioactive gases, while making the handling of the blades more manageable, is problematic. Copending patent application Ser. No. 13/612,905, filed Sep. 13, 2012, now issued U.S. Pat. No. 8,857,027, issued Oct. 14, 2014, overcomes this difficulty, but first requires a convenient way to the vertically segment the blades into four flat panels.
Therefore, for safe and cost effective shipment and storage of a spent boiling water reactor control rod a new apparatus is desired for vertically segmenting the control rod blades in an efficient manner to make the blades more amenable to further lateral segmentation to reduce the storage volume of the component to a manageable size that can be packaged in a dry cask.
Additionally, such an apparatus is desired that will minimize the release of radioactive debris in segmenting a boiling water reactor control rod.